Chosen Solution

When you use the mouse wheel, you can adjust in smaller steps than if you use the Ctrl++/Ctrl+- method.

Does it help?

You may want to try Firefox's zoom feature. [https://support.mozilla.com/en-US/kb/how-do-i-use-zoom How do I use Zoom? | How to | Firefox Help]
When you use the mouse wheel, you can adjust in smaller steps than if you use the Ctrl++/Ctrl+- method.
Does it help?

To zoom the page larger, you normally hold the Ctrl key and tap the + key on the numeric keypad.

If you have a laptop, there isn't a real numeric keypad, but you should find a set of extra numbers printed over the middle of your keyboard. This is the embedded number pad, and you should find both a + and a - key.

To use these keys, you usually have to hold the Fn key (or similar), so it is Ctrl+Fn++ to zoom larger, and Ctrl+Fn+- to zoom smaller.

Hope that helps clear it up.

Edit: Actually, the hyphen/underline key and the +/= key might also work, with no Fn key needed.

To zoom the page larger, you normally hold the Ctrl key and tap the + key on the numeric keypad.
If you have a laptop, there isn't a real numeric keypad, but you should find a set of extra numbers printed over the middle of your keyboard. This is the embedded number pad, and you should find both a + and a - key.
To use these keys, you usually have to hold the Fn key (or similar), so it is Ctrl+Fn++ to zoom larger, and Ctrl+Fn+- to zoom smaller.
Hope that helps clear it up.
Edit: Actually, the hyphen/underline key and the +/= key might also work, with no Fn key needed.